Oxygen demand is a significant parameter for determining the effect of organic pollutants in water. As microorganisms in the environment ingest the organic material, oxygen is depleted. This in turn can be harmful to fish and plant life. (http://www.spectronic.com/spectron/spctech2.htm). Wastewater from food processing is non-toxic but organic. High concentration of nutrients can be harmful for the environment. Extra quantities of nitrogen, fat and phosphorus require more oxygen for bacteria to decompose. If Chemical Oxygen Demand (COD)/Biochemical oxygen demand (B.O.D) content of the water is excessive, the oxygen supply in the water may be depleted below the level required to sustain aquatic life. (Ref: http://info.rfisk.is/verkefni/1077/hfe4f2.htm).
The Chemical Oxygen Demand (COD) determination is a measure of the oxygen equivalent of that portion of the organic matter in a sample that is susceptible to oxidation by a strong chemical oxidant under controlled conditions (American Public Health Association (APHA). (1998). In Standard methods for examination of water and wastewater. 20th Edn. American Public Health Association (APHA), American Water Works Association (AWWA), Water Pollution Control Federation (WPCF), Washington, D.C.).
The limitation of the test lies in its inability to differentiate between the biologically oxidizable and biologically inert material. COD determination has an advantage over BOD test in that the results can be obtained in less than five hours where as BOD requires 3 to 5 days. Further the test is relatively easy and with not much interference. (American Public Health Association (APHA), 1976). In: Standard methods for examination of water and wastewater. 14th edn American Public Health Association (APHA), American Water Works Association (AWWA), Water Pollution Control Federation (WPCF), Washington, D.C.).
The main chemical compounds in wastewater are Chemical Oxygen Demand (COD), nitrogen, phosphorus, fats, oils and grease. COD and BOD—5 are important parameters for measurement of organic matter content and oxygen needed to decompose the organic compounds. During the decomposition of organic matter there is less oxygen available in the sea and no oxygen in some places. It is possible to calculate COD or BOD into standard personal units, 60 g of oxygen to decompose the organic compounds from one person per day or equaling of 135 g of oxygen to decompose Chemical Oxygen Demand (COD) in waste water (COD=2.25×BOD). (Ref: http://info.rfisk.is/verkefni/1077/hfe—4f2.htm).
The calorimetric dichromate reflux method is commonly used method for determining the Chemical Oxygen Demand (COD) content in a sample, and has been preferred over procedures using other oxidants because of superior oxidizing ability, applicability to a wide variety of samples and ease of manipulation (American Public Health Association (APHA). (1989). In: Standard methods for examination of water and wastewater. 17th edn. American Public Health Association (APHA), American Water Works Association (AWWA), Water Pollution Control Federation (WPCF), Washington, D.C.). The basic principle involved is oxidizing the most types of organic matters by a boiling mixture of chromic and sulfuric acids. A sample is refluxed in strongly acid solution with a known excess of potassium dichromate (K2Cr2O7). After digestion, the remaining unreduced K2Cr2O7 is titrated with ferrous ammonium sulfate to determine the amount of K2Cr2O7 consumed and the oxidizable organic matter is calculated in terms of oxygen equivalent.
The determination of Chemical Oxygen Demand (COD) is widely used in municipal and industrial laboratories to measure the general level of organic contamination in waste water (Ref: http://www.chemetrics.com/lnstProd/COD.I.htm).
Wide ranges of instruments are available for Chemical Oxygen Demand (COD) estimation. CHEMetrics'—employs EPA (Environmental Protection Agency, USA) approved Dichromate reactor digestion method. (http://www.chemetrics.com/InstProd/COD.I.htm). Spectronic Instruments provide SPECTRONIC® Spectrophotometer and the Bioscience ACCU-Test® system based on APHA method. (American Public Health Association (APHA). (1989). In: Standard methods for examination of water and wastewater. 17th edn American Public Health Association (APHA), American Water Works Association (AWWA), Water Pollution Control Federation (WPCF), Washington, D.C.). It uses a semi-micro conversion of the Standard Methods procedure for the determination of Chemical Oxygen Demand (COD). (Ref: http://www.spectronic.com/spectron/spctech2.htm). In the North Dakota Department of Health (NDDH), Chemistry Division Chemical Oxygen Demand (COD) SOP (Ref: http://www.health.state.nd.us/lab/METHODS/I-4.HTM) COD determination is through comparison of absorbance for the standards and the samples in HACH COD reactor and Sequonic Turner model 390 Spectrophotometer.
ISCO-STP COD analyzers and the Phoenix analyzer uses ozone for rapid oxidation and provides continuous Chemical Oxygen Demand (COD) measurement corresponding directly to result of the laboratory standard dichromate method. (http://www.isco/html/prdprCOD.html).
Among the reference methods of Chemical Oxygen Demand (COD) determination, EPA method 410.1/410.2 and the Standard Method SM5220-D employ closed refluxing (Ref: http://splash.metrokc.gov/wir/enylab/LABGUIDE/cm_ref.htm). The biodegradability test—5-day and 28 day includes COD 5 and 15 day determinations in the reference OCED method 3101D—SOQ Appendix B Methods used by Burlington Research, Inc. (Ref: http://199.72.5.39/sogapb.htm).
PASTEL UV® system works exclusively in UV range of light spectrum with UV analyzer (Spectrophotometer). It requires 16 photodiodes and specially developed pulsed deuterium lamp. This analyzer requires calibration for accuracy within a very specific sample category such as industrial wastewater. For each additional application a new base line spectra has to be customized for specific samples. In this method the co-relation is only for BOD and TSS (Total Suspended Solids) which is 90% when compared to the traditional test methods. For COD the co-relation is valid only upto 6000 mg/L COD only. It is a indirect estimation based on reference data stored in internal UV based software (Ref.: http://www.azurenv.com/ispec.htm). The major limitations in different cases are the economics of the methods used, instruments employed and the time consumed. CHEMetrics' uses a standard digester block for heating the sample for 2 h at 150° C. In addition, the method needs to employ a Chemical Oxygen Demand (COD) Photometer (A-1051C) or Spectrophotometer which accepts a 16 mm diameter cell. The major limitation is that the results are not reportable to USEPA. On the other hand, 13 mm cells can be read in CHEMetrics VVR and A1051 photometer. However, the results are good for monitoring purposes only.
BioScience's EPA Accepted ACCU-TEST® method needs specific type of Chemical Oxygen Demand (COD) reagent vials, a heating block, data management software package, etc. are required. It makes each test quite costly. BioScience's EPA Accepted ACCU-TEST® is available only in a medium sensitivity ranges for Spectrophotometry 5 to 4500 mg/L Chemical Oxygen Demand (COD). In order to use the BioScience COD vials in the SPECTRONIC® 401, both the test tube holder and the Light shield are required where as the GENESYS™ 2 or GENESYS™ 5 require the cell holder Platform and its Test tube holder (Ref:http://www.spectronic.com/spectron/spctech2.htm).
In the North Dakota Department of Health (NDDH) Chemistry Division Chemical Oxygen Demand (COD.) SOP (Ref: http://www.health.state.nd.us/lab/METHODS/I-4.HTM) Chemical Oxygen Demand (COD) determination is in a narrow range of 0 to 150 and 150 to 1500 mg/L. The calorimetrically determined Chemical Oxygen Demand (COD) value is based on measuring the consumed oxidant in the chrome (Cr6+) and chromous (Cr3+) valence state. The method employs HACH COD reactor and Sequonic Turner model 390 Spectrophotometer. The spiking solutions in the 0 to 150 mg/L range are 10, 25, 50 and 150 where as for 150 to 1500 mg/L ranges, 5 concentration ranges 100, 250, 500, 1000 and 1500) are employed. It needs a sample volume of 10 ml, in addition to heating for 2 hours at 150° C.
In the Manganese III method for Chemical Oxygen Demand (COD) analysis (U.S. Pat. No. 5,556,787 September, 1996) determination is done by using an analysis reagent comprised of a mixture of stabilized Manganese III ion and an inorganic non-oxidizing acid such as sulfuric or phosphoric acid. The method involves titration and calorimetric determination. The method involves digestion of the test sample by heating between 100 to 200° C. for up to 2 hours.
A method based on redox cell involved treatment of organic carbon with an excess of an oxidizing agent. The remaining oxidizing agent is determined in a redox cell to ascertain how much of the oxidizing agent was consumed by the organic carbon. This was the COD. This is multi-step process involving a large number of reagents (U.S. Pat. No. 3,930,798 January, 1976). Another redox based method involves ozone as an oxidizing agent (U.S. Pat. No. 5,324,666 June, 1994). The accuracy of the process is limited only by the control range of the ozone generating pumps. It can work within a range of less than 0.5 ozone load i.e. the ratio of chemical oxygen demand to added ozone. By increasing the ozone input the measuring range may be extended upwards but with reduced accuracy.
All the methods employed so far have long refluxing or digestion periods and are followed by titration or spectrophotometric reading of the standards and the samples at different wavelengths.
In the present invention the major limitations involved in estimation of chemical oxygen demand of water and wastewater have been over come. The novelty of the present invention is in use of a rapid, simple and effective method for estimation of COD of a wide range of samples. Another novelty of the present invention is the reduction in time period taken for estimation of COD, from 2 h to less than 5 minutes. In the present invention, parameters have been studied for preparation of a reaction mixture, which is easy to handle. Another novelty of the present invention is in the use of very small quantities of reagents and the test sample. In the present invention the various reaction mixtures can be read instantly for a very wide range of COD loads by using minor equipment e.g. photometer. Another novelty of the present invention is the ability to conduct the estimation on site, avoiding any possible changes in the test sample quality. Yet another novelty of the present invention is the COD color chart is used for determination of COD. over a wide range. Another novelty of the present invention is the flexibility to use reagents for determination of COD. over a wide range. Another novelty of the present invention is the simplicity for preparing reference standards easily and rapidly. Another novelty of the present invention is the stability of color based reference standards for long period without preserving them at low temperatures. These can thus be used repeatedly.